Since its early prediction by A. E. Kaplan (Pis'ma Zh. Eksp. Teor. Fiz. 9, 58 (1969) [JETP Lett. 9, 33 (1969)]), self-deflection of optical beams has been considered one of the most exciting manifestations of nonlinear optics: a single beam propagating in a nonlinear medium develops an asymmetric profile and consequently curves (and carves) its own trajectory. The beam intensity determines the beam trajectory.
If self-deflection had been accomplished with low power levels, fast response times, and many resolvable spots, this fascinating process would have already found its way into commercial products, in applications ranging from optical interconnects to laser printers, optical scanners, routers, and optical limiters. Unfortunately, experimental demonstrations of self-deflection of optical beams have been scarce, exhibiting very few resolvable deflection spots. A resolvable spot of deflection is defined as the deflection angle divided by the diffraction angle of the finite beam.
Thus far, self-deflection has been demonstrated in NaCl and CdSSe crystals, liquid CS2, sodium vapor and nematic liquid-crystal films.
In all of these attempts at self-deflection, the number of resolvable spots was small: typically 2-3, with the exception of sodium vapor, which had 8. Furthermore, all of these experiments required high intensities, ranging from 200 W/cm2 in sodium to 400 MW/cm2 in NaCl. All of these early demonstrations of self-deflection suffered from major distortions of the beam profile, which limited the deflection angle.
By contrast, the present invention provides very large self-deflection of optical beams. The self-deflection arises from enhanced photorefractive effects in photorefractive semiconductors. For example, CdZnTe:V (Cadmium Zinc Tellurium doped with Vanadium) has been shown to result in up to 27 resolvable deflection spots at 1 Watt/cm2 intensity, more than 3 times the resolvable spots than in any reported prior art self-deflection results, and at 200 times lower intensity.
These deflections arise from enhanced photorefractive effects in photorefractive semiconductors, giving rise to optically-induced index changes, typically in excess of 0.008.
The index change highly depends on the intensity of the deflected beam, hence the self-deflection. The deflection can be controlled through the intensity of a second (“background”) beam at a different wavelength, thereby the process also allows for all-optical control of one beam with another. The deflection can also be controlled through the bias electric field applied to the crystal, thus the same process also facilitates electro-optic deflection. However, in a sharp contradistinction with “traditional” electro-optic deflection yielding 1-5 resolvable spots, our process yields more than 25 spots. In principle, our self-deflection technique can be further improved to facilitate more than 100 resolvable spots (see details below).
Another advantage of the present invention is that, in contrast to prior art, the deflected beam has a symmetric (circular) structure throughout almost the entire deflection range.
In summary, it is a main object of the present invention to provide a system and method for self-deflection of an optical beam (where modifying the intensity of the beam varies the beam trajectory).
It is another main object of the present invention to switch and deflect one beam by varying the intensity of another beam (all-optical beam steering).
It is another main object of the present invention to provide control of the deflection by varying the level of electrical bias.
All of these methods of deflecting, steering, controlling, and modulating optical beams rely on using a proper combination of light and bias field to enhance the optical nonlinearity in a photorefractive semiconductor and consequently modulate, steer, and deflect an optical beam using light, electricity, or both.
Other objects and advantages of the present invention will become apparent after reading the present specification and reviewing the accompanying drawings.